System for monitoring characteristic parameters of a tyre

ABSTRACT

A system for sensing at least one characteristic parameter of a tyre fitted to a vehicle includes a movable unit and a fixed unit. The movable unit is combined with the tyre and includes a device for sensing the at least one characteristic parameter, a device for transmitting a signal out of the tyre that relates to the at least one characteristic parameter, and a device for generating electrical energy. The fixed unit is combined with the vehicle and includes a device for receiving signals from the movable unit. The electrical energy generating device is capable of supplying electrical energy to the sensing device and to the transmitting device. The electrical energy generating device includes a capacitor that charges itself with electrical energy in response to mechanical stresses applied to the tyre. The movable unit and a vehicle wheel are also disclosed.

The present invention relates to a system for monitoring characteristicparameters of a tyre fitted to a vehicle.

In particular, the present invention relates to the possibility ofsensing characteristic parameters, such as for example pressure,temperature and accelerations, inside a tyre using a sensor placedinside the tyre itself.

A wheel is the connection between the vehicle and the road; it performsthe function of providing pneumatic suspension for the vehicle and itsload and providing, through the tyre, satisfactory behaviour on theroad. The suspension of the vehicle is provided by the volume ofcompressed air contained inside the wheel.

A tyre comprises an internally hollow toroidal structure formed by aplurality of components, in the first place a textile or metalliccarcass ply, the edges of which are attached to at least one pair ofannular reinforcing cores known as bead wires, which arecircumferentially inextensible and are inserted in two beads eachdefined along an internal circumferential edge of the carcass in orderto anchor the tyre to the corresponding supporting rim.

The carcass ply includes a supporting structure that runs axially fromone bead to the other to form a toroidal structure comprising aplurality of textile or metallic cords embedded in a layer ofelastomeric material. In tyres of the so-called “radial” type, theabovementioned cords essentially lie in planes containing the axis ofrotation of the tyre.

Forming a ring around this carcass are an annular superstructure knownas the belt structure, normally made up of one or more strips ofrubberized fabric wound on top of each other to define a so-called “beltpack”, and a tread band of elastomeric material wrapped around the beltpack and moulded with a relief design for rolling contact of the tyrewith the road. Two elastomeric side walls are also placed on thecarcass, in axially opposite lateral positions, each extending radiallyoutwards from the outer edge of the corresponding bead.

In tyres of the so-called “tubeless” type, i.e. those that require noinner tube when in use, the inside surface of the carcass is normallycovered with a so-called “liner”, which is one or more layers ofelastomeric material impermeable to air. Lastly, the carcass can includeother known components, i.e. edges, shims and fillers depending on theparticular design of tyre.

A pneumatic vehicle wheel comprises a tyre defining a toroidal cavityand mounted on a corresponding rim, which has a bottom surface providedwith a central well and two bead seats against which the tyre beads comeinto abutment and which are each axially defined between an extremeradial surface (shoulder) in an axially external position and anopposing, axially internal, annular projection which locks the bead onthe corresponding seat.

In a “tubeless” tyre, the compressed air is contained between the tyreand the supporting rim. The liner on the inside surface of the tyrekeeps the air at pressure inside the tyre. This tyre is inflated throughan inflation valve which is usually positioned on the drop centre ofsaid rim.

A tyre of this type is described for example in Patent ApplicationEP928680.

Another way of maintaining the suspension capacity of the tyre is to usean inner tube inserted between the tyre and the rim and inflated withcompressed air which is injected into the tube through an inflationvalve projecting out through the wheel.

The inner tube, inserted between the tyre and rim, comprises a tubularbody expandable to give toric shape. It is generally made of elastomericmaterial and inflates through an inflation valve.

The inflation valve of the inner tube usually includes a base forattachment to the inner tube and a cylindrical envelope (shank) fixed tothe base and containing the mechanism that has to be activated forinflation and deflation operations.

An incorrectly inflated tyre reduces the efficiency of the vehicle: inparticular, it causes increased fuel consumption, poorer handling andgreater tyre wear, to cite only a few of the most serious drawbacks.

It is therefore of the greatest importance to be able to continuallymonitor the pressure in the tyres of the vehicle. Also, if it is wishedto check the behaviour of a moving tyre, other parameters can bemonitored, such as, for example, the accelerations and deformations thattake place within a tyre.

U.S. Pat. No. 5,540,092 discloses a system for monitoring the pressurein a tyre comprising a pressure sensing unit and a unit for transmittingan encoded signal to the vehicle on which the tyre is fitted. Thetransmitting unit may be mounted inside or outside of the tyre. Thetransfer of this coded signal takes place by inductive coupling betweenthe transmission unit and a fixed antenna. A battery powers thistransmission unit.

U.S. Pat. No. 5,562,787 discloses a method for monitoring the conditionsof a vehicle tyre, e.g. the pressure and temperature of the air in thetyre. The method uses a programmable self-powered device mounted on theinside surface of the tyre or inserted in the wall of the rim on whichsaid tyre is mounted. The device comprises a power source that can bemade active or inactive using a switching device, a sensor formonitoring said information, an integrated circuit, an amplifier and anantenna. A transmitter-receiver located on the vehicle or in a remoteposition interrogates the programmable self-powered device, whichanswers with a radio-frequency signal containing the requiredinformation. The programmable self-powered device is activated by saidremote transmitter/receiver which instructs the switching device to makethe power source active.

U.S. Pat. No. 6,217,683 discloses a tyre monitoring device in which amodule for monitoring information about the state of the tyre isinserted in the tyre itself and attached to the inside surface of thetyre by a fixing mechanism. This fixing mechanism comprises a fixed partattached to the surface of the tyre carcass, and another part attachedto said module. Said first and second parts together keep said module incontact with the inside surface of the tyre carcass. One application ofthe monitoring system is to measure the tyre pressure. The measurementis transmitted to the outside by radiofrequency signal.

Patent application WO 9929524 discloses a tyre pressure sensorencapsulated in elastomeric material and attached in the toroidal zoneof the tyre, preferably in the vicinity of the equatorial plane of saidtyre. The sensor is attached to the inner surface of the tyre by anadhesive or is attached by the curing of the elastomeric material duringmanufacture of the tyre.

The Applicant has observed that the abovementioned methods for measuringcharacteristic parameters of a tyre require devices for transmitting outof the tyre a signal corresponding to the measurements made.

The Applicant has seen that the amount of information associated withthe sensing of characteristic parameters of a tyre is such as to requirethe transmission of a signal having an extended pass-band. Inparticular, in order to transmit a signal from the tyre, such as anacceleration signal, which can be decoded outside of the tyre andinterpreted in a meaningful way, sampled transmission of this signalmust occur at a frequency of at least 6 kHz (at least one sample every1.6×10⁻⁴ sec).

For example, each sample requires the transmission of at least 10 Bits(8 bits of information plus 2 control bits), thus necessitating thetransmission of 60 000 bits/sec.

The transmission of so much information requires a large amount ofelectrical power which must be supplied on the inside of the tyre, forexample by a battery, continuously over a long period of time, if, forexample, the intention is to monitor tyre deformations in order tocontrol the motion of the vehicle.

Also, the Applicant has observed that to transmit such an amount ofinformation from inside the tyre requires, for example, 0.5 watts ofelectrical power to be available inside the tyre. This electrical powercan only be supplied by a large, heavy battery, which could only beinserted with difficulty into a tyre.

The Applicant has found that by generating the electrical energynecessary to sense these parameters, code the corresponding signals andtransmit these signals following coding or preprocessing inside thetyre, there is no need to use batteries requiring periodical replacementand the consequent work of a technician trained to carry out thisreplacement. This electrical energy is conveniently generated byexploiting the movement of the tyre.

The movable unit is of small dimensions and limited weight and thereforehas little influence on the behaviour of the tyre while the vehicle isin motion. The Applicant has used an MEMS technology(Micro-Electro-Mechanical Systems) whereby mechanical components andelectronic components can be integrated on the same substrate (wafer).To make a device with MEMS technology, a wafer is used, preferably ofsilicon, on which micromechanical structures integrated with electronicstructures for controlling/processing an electrical signal connectedwith said mechanical structure are made by photolithography followed bychemical etching.

A first aspect of the present invention relates to a system for sensingat least one characteristic parameter of a tyre fitted to a vehiclecomprising:

-   -   a movable unit combined with said tyre,    -   said movable unit comprising a device for sensing said at least        one characteristic parameter and a device for transmitting out        of the tyre a signal relating to said at least one        characteristic parameter,    -   a fixed unit combined with said vehicle that includes a device        for receiving from said movable unit,        characterized in that

said movable unit comprises an electrical energy generating devicecapable of supplying said sensing device and said transmitting device,that comprises a capacitor that charges itself with electrical energy inresponse to the mechanical stresses applied to said tyre.

Preferably, said capacitor comprises a fixed plate and a movable platewhich move with respect to each other in response to said stresses.

Preferably, said fixed plate and said movable plate can vary theirdistance in response to said stresses.

Preferably, said fixed plate and said movable plate are connected toeach other by a pair of springs.

In particular, said fixed plate and said movable plate are connected toa fixed support and to a movable support, respectively.

Preferably, the movement of this movable plate is bounded by a pair ofend stop elements.

Preferably, said sensing device, said transmitting device, saidprocessing unit and said generating device are produced on a substrate.

Preferably, said movable unit is produced by MEMS technology.

Another aspect of the present invention relates to a movable unit forsensing at least one characteristic parameter of a tyre fitted to avehicle comprising a device for sensing said at least one characteristicparameter and a device for transmitting out of the tyre a signalrelating to said at least one characteristic parameter,

characterized in that it comprises an electrical energy generatingdevice capable of supplying said sensing device and said transmittingdevice, that comprises a capacitor that charges itself with electricalenergy in response to the mechanical stresses applied to said tyre.

Another aspect of the present invention relates to a vehicle wheelcomprising

-   -   a tyre,    -   a supporting rim for said tyre, and    -   a movable unit combined with said tyre comprising a device for        sensing at least one characteristic parameter of said tyre and a        device for transmitting out of the tyre a signal relating to        said at least one characteristic parameter,        characterized in that said movable unit comprises an electrical        energy generating device capable of supplying said sensing        device and said transmitting device, that comprises a capacitor        that charges itself with electrical energy in response to the        mechanical stresses applied to said tyre.

Other features and advantages will be found in the detailed descriptionof a preferred but not exclusive embodiment of the present invention inits various aspects.

This description will be given below with reference to the attacheddrawings, which are supplied purely for guidance and are therefore notlimiting. In the drawings:

FIG. 1 is a cross section through a tyre mounted on its supporting rimwith a movable unit inserted inside it;

FIG. 2 is a block diagram of a fixed unit of said sensing systemaccording to the invention combined with a vehicle;

FIG. 3 is a block diagram of said movable unit of said sensing systemaccording to the invention combined with a tyre;

FIG. 4 is a schematic 3-dimensional exploded view of said movable unit;

FIG. 5 is a schematic exploded view of a device for generatingelectrical energy built into said movable unit.

FIG. 1 shows by way of example a wheel 1 comprising a tyre 11, of thetype conventionally known as “tubeless”, that is having no inner tube,and a supporting rim 12. This tyre is inflated through an inflationvalve 13 which by way of example is positioned, in a manner known perse, on the drop centre of said rim.

The tyre consists of an internally hollow toroidal structure formed by aplurality of components—in the first place by a textile or metalliccarcass having two beads 14 and 14′ each defined along an internalcircumferential edge of the carcass in order to hold the tyre on itssupporting rim 12. Said carcass comprises at least one pair of annularreinforcing cores 15 and 15′ known as bead wires, which are inserted insaid beads.

The carcass includes a supporting structure made up of a reinforcing ply16 containing textile or metallic cords. This ply is laid axially fromone bead to the other to give a toroidal profile, and its edges are eachconnected to a corresponding bead wire.

In the so-called radial type of tyre, the above cords lie more or lessin planes containing the axis of rotation of the tyre.

Forming a ring around this carcass are an annular structure 17, known asthe belt structure, normally made up of one or more strips of rubberizedfabric wound on top of each other to define a so-called “belt pack”, anda tread band 18 of elastomeric material wrapped around the belt pack andmoulded with a relief design for rolling contact of the tyre with theroad. Two elastomeric side walls 19 and 19′ are also placed on thecarcass, in axially opposite lateral positions, each extending radiallyoutwards from the outer edge of the corresponding bead.

In the so-called “tubeless” type of tyre, the inside surface of thecarcass is normally covered with a liner 111, that is one or more layersof elastomeric material impermeable to air. Lastly, the carcass caninclude other known components, that is edges, shims and fillersdepending on the particular design of the tyre.

Together, these components determine the mechanical characteristics ofelasticity, stiffness and resistance to deformation of the tyre, whichconstitutes the connection between the system of forces applied to thetyre and the magnitude of the corresponding deformations it undergoes.

It should be pointed out that, for the purposes of the presentdescription, the term “elastomeric material” means a compound formedfrom at least one polymer base appropriately amalgamated withreinforcing fillers and/or process additives of various types.

The system for monitoring characteristic parameters of a tyre fitted toa vehicle, according to the present invention, comprises a fixed unit 2preferably located in said vehicle and a movable unit 3 combined withsaid tyre.

FIG. 2 is a block diagram of said fixed unit 2, preferably comprising areceiving device 21 for receiving signals from said movable unit, and areceiving antenna 22.

The receiving device preferably comprises a radiofrequency receiverconnected to said antenna and preferably also an electrical demodulatordevice.

The electrical energy required to supply said fixed unit may preferablybe supplied directly by the battery of the vehicle via a suitable drivecircuit (not shown). In addition, said fixed unit advantageouslycommunicates with suitable devices mounted on board the vehicle fordisplaying said sensed parameters. For example, the inflation pressuremay advantageously be displayed on the dashboard of the vehicle on aspecial display.

Said movable unit 3, illustrated in a block diagram in FIG. 3, comprisesa transmitting device 31 for transmitting signals to said fixed unit anda sensing device 32 for sensing characteristic parameters of a tyre—thiscomprises at least one sensor for measuring these parameters.

Examples of said at least one sensor are a pressure sensor, atemperature sensor, an acceleration sensor, a sensor of rotary movement(the number of revolutions of the tyre) or combinations of these.

This movable unit also includes a processing unit (processor) 34 and amemory device 35. This memory device may contain pre-stored instructionsfor the processing unit and may also contain rewritable memory locationsin which information about the measurements taken by the sensors can bestored. A device for distributing the electrical energy 36 preferablydistributes appropriately to said processing unit, said memory device,said device for transmitting to said fixed unit, and said device forsensing the electrical energy necessary for their operation.

Within this movable unit, the signals sensed by the sensors can besuitably coded or pre-processed for transmission out of the tyre. Forexample, they may be associated with a code identifying the particulartyre, to avoid confusion with similar signals coming from the othertyres of the vehicle.

In accordance with the present invention, this coding or pre-processingalso makes it possible to send out of the tyre, by means of saidtransmission device, a pre-processed signal containing a quantity ofinformation compatible with the capacity of a receiver outside of thetyre to interpret this signal in a meaningful way.

For the purposes of the present invention, meaningful interpretation ofthis signal means that from said signal a decoding device external tothe tyre, e.g. contained in the fixed unit, is able to reconstruct theprofile of the sensed signal in order to determine for example theminima and maxima.

An example of coding or pre-processing is set out below for a signalrelating to the triaxial acceleration of a point on the tyre (withreference to a system of three Cartesian axes x, y and z).

This signal represents the three components of the acceleration of thispoint a_(x), a_(y) and a_(z) relative to said system of three Cartesianaxes. Said signal is preferably filtered (for example by a “low pass”filter to filter out the non-significant high frequencies). An RMS (RootMean Square) calculation can also be performed, that is a calculationthat gives an instantaneous indication of how much the maximum value ofthe signal differs from its mean value. Another processing stepdifferentiates the signal with respect to time in order to find themaximum and its mean value. These processing steps are preferablycarried out after the signal received from the corresponding sensor hasbeen converted into a digital signal, as these digital operations can bedone by software simply by retrieving from said memory a storedprocedure containing instructions for said processing unit.

Having obtained values, expressed in digital form by a suitable numberof bytes, in the example described, these are compared with each otherto calculate the coefficient of friction between the tyre and the ground(and this in turn will be expressed by a suitable number of bytes). Thisnumber is sent to the transmitter, and the transmitter transmits it tothe fixed unit mounted in the vehicle.

Other pre-processing steps are carried out for example on a signalcorresponding to a pressure reading, which can be compared with anominal correct inflation pressure for a given temperature pre-stored inthis non-volatile memory. The result of this comparison may be sent outof the tyre only if the actual inflation pressure departs from thenominal pressure by a predetermined value.

This movable unit is preferably made by MEMS (Micro-Electro-MechanicalSystems) technology. This technology makes it possible to integratemechanical and electronic components on the same substrate (wafer) in anextremely small amount of space. To make a device using MEMS technology,micromechanical structures integrated with electronic structures capableof controlling/processing the electrical signal connected with saidmechanical structure are produced, by photolithography followed bychemical etching, on a substrate, preferably of silicon.

An example of MEMS technology is described, for example, in the documenttitled “Adapting multichip module foundries for MEMS packaging”published by the International Journal of Microcircuits and ElectronicPackaging, Vol. 21. No. 2, pp. 212-218, published in 1998.

The main advantage of MEMS technology is the ability to create extremelysmall structures on a mass-production scale. For example, it is possibleto produce simultaneously on a single wafer of silicon, thousands ofcopies of the same MEMS component. In addition, the individualcomponents are advantageously made from single-crystal silicon and itsoxide. In this way the quality of the surfaces obtained makes thecharacteristics of the components almost “ideal” in terms of mechanicalstrength.

By way of example, we set out below the steps necessary to create a MEMSaccelerometer sensor which is made by creating a small “suspended mass”on the surface of said silicon wafer. These steps comprise:

-   -   drawing on said wafer, by photolithographic processes, an area        that corresponds to the suspended mass and its support element;    -   doping said area with chemical agents, such as boron or silicon        oxide, and then immersing it in hydrofluoric acid to make it        relatively inert to chemical etching;    -   chemically etching the wafer to remove the silicon from around        the mass and its support, creating an open channel around the        mass;    -   generating a small cavity, on which said mass is left suspended;        and    -   creating around said cavity, by processes similar to those used        for the manufacture of integrated circuits, circuits capable of        measuring the distance between the suspended mass and the bottom        of the cavity in which it is inserted.

This distance corresponds to a measure of the force acting on the masswhich deflects the support of the mass, and hence gives a measure of theacceleration.

An accelerometer produced by this method occupies a volume, inclusive ofits control electronics, of no more than 2.5×2.5×0.25 mm. Thus, on a 6″silicon wafer, 1500-2000 accelerometers can be produced.

A pressure sensor contained in said sensing device can be produced byMEMS techniques, by creating a silicon diaphragm which is deformed bythe pressure of the air inside the tyre acting on an exposed face. Thedeformation is measured as a change in the capacitance between thediaphragm and a fixed conducting surface.

An acceleration sensor can similarly be produced by MEMS techniques, byinserting into a silicon diaphragm a mass which, when subjected toacceleration, undergoes the action of a force equal to the product ofthe mass under the acceleration. As before, the deformation of thediaphragm can be measured as a change in capacitance.

In general, all the abovementioned sensors can be made by MEMStechnology on the same substrate. Similarly, MEMS technologies can beused to produce on this substrate in accordance, for example, with thediagram FIG. 4, all the devices that comprise the movable station.

One possible structure for said movable unit is described in FIG. 4. Inparticular, said movable unit is preferably made on a substrate, onwhich the various components are arranged.

The movable unit in FIG. 4 preferably comprises an electricalenergy-generating device 33 that generates electrical energy in responseto the stresses to which the movable unit is subjected (such ascentrifugal force or the deformations of the inner surface of the tyre).This device is preferably made on the same substrate as the sensors, theprocessing unit (processor) 34 and the memory device 35.

The device can be made using a MEMS technology. In particular, it isknown from the document titled “Development of an ElectromagneticMicrogenerator” published in the journal Electronics Letters, August1997 that as soon as two plates of a capacitor move with respect to eachother, provided the electric charge (previously supplied to thecapacitor) passing through the plates is constant, the voltage betweenthe two plates increases.

In accordance with the present invention, a system is produced insidethis substrate in which one plate of the capacitor is fixed and thesecond is connected to a damping spring. When a vibration is applied tothe “oscillating” surface of the second plate, the capacitor pumpselectrical energy from a low potential level to a higher level. Thehigher potential can advantageously then be stored in an isolatedcapacitive vessel for use as necessary.

An example of this device created on a substrate as described above isillustrated in FIG. 5. This device comprises two fixed supports 51, 51′,to each of which a fixed metal plate 52 or 52′ is attached, and amovable support 53 to which a movable metal plate 54 is attached.

Said movable support is connected to said two fixed supports by twosprings 55 and 55′. This pair of springs allows the movable support 53and the movable plate 54 to move in two directions, indicated in FIG. 5by the double arrow F. The movement of this movable support in saiddirection is limited by two opposing end stops 56 and 56′. Said twofixed supports 51, 51′ are preferably attached to said substrate (notshown in FIG. 5). When the tyre is rolling, the stresses to which it issubject bring about the abovementioned movement of the movable platerelative to the two fixed plates, generally in the two directions of thedouble arrow F, FIG. 5. The movable and fixed plates form a capacitorhaving a predetermined charge capacity. The capacitor can be pre-chargedbefore the movable unit is placed in the tyre by briefly supplying avoltage to the capacitor. The stresses acting on the moving tyre,especially those due to the acceleration and deceleration of the tyre,generate the abovementioned movement of the plates setting up apotential difference at the terminals of the capacitor. The potentialdifference obtained is stored in the distribution device 36 which makesit available to the other devices of the movable unit.

The substrate may be large covered by an external coating that extendspreferably over the entire surface area of said movable unit except fora portion corresponding to the position of the sensitive areas of thesensors, as these areas must be in communication with the volume inwhich said characteristic parameters are being measured.

This external coating serves to produce an essentially stable bondbetween said movable unit and the inner surface of the tyre.

This movable unit is preferably attached to the inner surface of thetyre in the crown area of the tyre by a suitable adhesive which willensure that the abovementioned stresses acting on the tyre do not detachthe unit from the inner surface of the tyre.

The movable unit is small and lightweight. It weighs preferably lessthan 5 grams and has a maximum occupied volume of 2 cm³. Such a movableunit will not influence the balance of the tyre when rotating.

1-11. (canceled)
 12. A system for sensing at least one characteristicparameter of a tyre fitted to a vehicle, comprising: a movable unit; anda fixed unit; wherein the movable unit is combined with the tyre,wherein the movable unit comprises: a device for sensing the at leastone characteristic parameter; a device for transmitting a signal out ofthe tyre; and a device for generating electrical energy; wherein thesignal relates to the at least one characteristic parameter, wherein thefixed unit is combined with the vehicle, wherein the fixed unitcomprises a device for receiving signals from the movable unit, whereinthe electrical energy generating device is capable of supplyingelectrical energy to the sensing device, wherein the electrical energygenerating device is capable of supplying electrical energy to thetransmitting device, and wherein the electrical energy generating devicecomprises a capacitor that charges itself with electrical energy inresponse to mechanical stresses applied to the tyre.
 13. The system ofclaim 12, wherein the capacitor comprises: a fixed plate; and a movableplate; wherein the fixed plate and the movable plate move with respectto each other in response to the mechanical stresses.
 14. The system ofclaim 13, wherein a distance between the fixed plate and the movableplate can vary in response to the mechanical stresses.
 15. The system ofclaim 13, wherein the fixed plate and the movable plate are connected toeach other by a pair of springs.
 16. The system of claim 13, wherein thefixed plate is connected to a fixed support, and wherein the movableplate is connected to a movable support.
 17. The system of claim 13,wherein movement of the movable plate is bounded by a pair of end-stopelements.
 18. The system of claim 12, wherein the sensing device, thetransmitting device, and the generating device are produced on asubstrate.
 19. The system of claim 18, wherein the movable unit isproduced by micro-electro-mechanical systems (MEMS) technology.
 20. Thesystem of claim 18, wherein a processing unit is also produced on thesubstrate.
 21. The system of claim 20, wherein the movable unit isproduced by micro-electro-mechanical systems (MEMS) technology.
 22. Thesystem of claim 18, wherein a memory device is also produced on thesubstrate.
 23. The system of claim 22, wherein the movable unit isproduced by micro-electro-mechanical systems (MEMS) technology.
 24. Thesystem of claim 18, wherein an electrical energy distributing device isalso produced on the substrate.
 25. The system of claim 24, wherein themovable unit is produced by micro-electro-mechanical systems (MEMS)technology.
 26. The system of claim 18, wherein a processing unit and amemory device are also produced on the substrate.
 27. The system ofclaim 26, wherein the movable unit is produced bymicro-electro-mechanical systems (MEMS) technology.
 28. The system ofclaim 18, wherein a processing unit, a memory device, and an electricalenergy distributing device are also produced on the substrate.
 29. Thesystem of claim 28, wherein the movable unit is produced bymicro-electro-mechanical systems (MEMS) technology.
 30. A movable unitfor sensing at least one characteristic parameter of a tyre fitted to avehicle, comprising: a device for sensing the at least onecharacteristic parameter; a device for transmitting a signal out of thetyre; and a device for generating electrical energy; wherein the signalrelates to the at least one characteristic parameter, wherein theelectrical energy generating device is capable of supplying electricalenergy to the sensing device, wherein the electrical energy generatingdevice is capable of supplying electrical energy to the transmittingdevice, and wherein the electrical energy generating device comprises acapacitor that charges itself with electrical energy in response tomechanical stresses applied to the tyre.
 31. A vehicle wheel,comprising: a tyre; a supporting rim for the tyre; and a movable unitcombined with the tyre; wherein the movable unit comprises: a device forsensing at least one characteristic parameter of the tyre; a device fortransmitting a signal out of the tyre; and a device for generatingelectrical energy; wherein the signal relates to the at least onecharacteristic parameter, wherein the electrical energy generatingdevice is capable of supplying electrical energy to the sensing device,wherein the electrical energy generating device is capable of supplyingelectrical energy to the transmitting device, and wherein the electricalenergy generating device comprises a capacitor that charges itself withelectrical energy in response to mechanical stresses applied to thetyre.